How to calculate percentage improvement in response time for performance testing

Question

How should I calculate the percentage improvement in response time.

I am getting 15306 ms response time for old code and 799 ms response for th

Answer 1

I think the answers above suffer from the original question not having nice round numbers and that there are 3 different ways to state the result.

Let's assume that the old time was 10 seconds and the new time is 5 seconds.

There's clearly a 50% reduction (or decrease) in the new time:

(old-new)/old x 100% = (10-5)/10 x 100% = 50%

But when you talk about an increase in performance, where a bigger increase is clearly better, you can't use the formula above. Instead, the increase in performance is 100%:

(old-new)/new x 100% = (10-5)/5 x 100% = 100%

The 5 second time is 2x faster than the 10 second time. Said a different way, you can do the task twice (2x) now for every time you used to be able to do it.

old/new = 10/5 = 2.0

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So now let's consider the original question

The old time was 15306 ms and the new time is 799 ms.

There is a 94.7% reduction in time.

(old-new)/old x 100% = (15306-799)/15306 x 100% = 94.7%

There is a 1816% increase in performance:

(old-new)/new x 100% = (15306-799)/799 x 100% = 1815.6%

Your new time is 19x faster:

old/new = 15306/799 = 19.16